PVDF-based paints have been used since more than four decades for the coil painting for architecture as they are capable to produce high performance coatings.
Generally, the PVDF-based painting compositions comprise pigments, resins, generally acrylic resins, and various additives and can be applied in a liquid form, when formulated in water or in particular solvents, or in powder form.
Known high performance paints used for coatings in architecture are PVDF based dispersions, having particles with an average diameter between 150 to 350 nm prepared by emulsion polymerization in the presence of a surfactant formed of a mixture of perfluoroalkanoic acids having a chain length between 7 and 13 carbon atoms and average molecular weight of about 480. Said surfactant is commercially known as Surflon™ S111 (Asahi Glass). The PVDF dispersion prepared by polymerization by using this fluorosurfactants mixture is coagulated, and the polymer is then washed, dried in a spray dryer and then formulated with other additives to obtain the paint.
Nevertheless, recently, perfluoroalkanoic acids, in particular those having 8 or more carbon atoms, have raised environmental concerns. For instance, perfluoroalkanoic acids have been found to show bioaccumulation. Accordingly, efforts are now devoted to phasing out from such compounds and methods have been developed to manufacture fluoropolymer products using alternative surfactants having a more favourable toxicological profile.
Several approaches have been recently pursued to this aim, typically involving either non fluorinated, partially fluorinated or even perfluorinated surfactants, these latter typically comprising perfluoroalkyl linear or cyclic chains interrupted by one or more catenary oxygen atoms, said chains having an ionic carboxylate group at one of its ends.
Nevertheless, all these surfactants do not possess suitable nucleating behaviour for providing VDF polymer particles having suitable sizes; these surfactants thus fail to enable tuning particle size of the latex in the range suitable for paints formulation.